Editing White dwarf (section)

==== Metal-rich white dwarfs ====
[[File:Periodic Table White Dwarfs.png|thumb|Elements discovered in the atmosphere of white dwarfs colder than {{val|25000|u=K}}.]]
Around 25–33% of white dwarfs have metal lines in their spectra, which is notable because any heavy elements in a white dwarf should sink into the star's interior in just a small fraction of the star's lifetime.<ref name=":0">{{cite journal |title=Extrasolar Cosmochemistry |journal=Annual Review of Earth and Planetary Sciences |date=2014-01-01|pages=45–67 |volume=42 |issue=1 |doi=10.1146/annurev-earth-060313-054740 |first1=M. |last1=Jura |first2=E.D. |last2=Young |bibcode=2014AREPS..42...45J|doi-access=free }}</ref> The prevailing explanation for metal-rich white dwarfs is that they have recently accreted rocky [[planetesimal]]s.<ref name=":0" /> The bulk composition of the accreted object can be measured from the strengths of the metal lines. For example, a 2015 study of the white dwarf Ton 345 concluded that its metal abundances were consistent with those of a [[Planetary differentiation|differentiated]], rocky planet whose mantle had been eroded by the host star's wind during its [[asymptotic giant branch]] phase.<ref>{{cite journal |title=The composition of a disrupted extrasolar planetesimal at SDSS J0845+2257 (Ton 345) |journal = Monthly Notices of the Royal Astronomical Society |date=2015-08-11|pages=3237–3248 |volume=451 |issue=3 |doi=10.1093/mnras/stv1201 |language=en |first1=D.J. |last1=Wilson |first2=B.T. |last2=Gänsicke |first3=D. |last3=Koester |first4=O. |last4=Toloza |first5=A. F. |last5=Pala |first6=E. |last6=Breedt |first7=S.G. |last7=Parsons |doi-access = free |arxiv=1505.07466 |bibcode=2015MNRAS.451.3237W|s2cid=54049842 }}</ref>